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  Light emitting diode and method for manufacturing the sameRelated Patent Categories: Semiconductor Device Manufacturing: Process, Making Device Or Circuit Emissive Of Nonelectrical Signal, Packaging (e.g., With Mounting, Encapsulating, Etc.) Or Treatment Of Packaged Semiconductor, Having Additional Optical Element (e.g., Optical Fiber, Etc.)The Patent Description & Claims data below is from USPTO Patent Application 20070087461. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATION [0001] The invention is a division of the application filed on Jul. 22, 2004, with an application Ser. No. 10/895,893 and entitled "LIGHT EMITTING DIODE AND METHOD FOR MANUFACTURING THE SAME". The subject matters of the above-identified application are incorporated by reference herein. FIELD OF THE INVENTION [0002] The present invention relates to a light emitting diode, and more particularly, to a high-brightness light emitting diode manufactured by a wafer bonding technique. BACKGROUND OF THE INVENTION [0003] Referring to FIG. 1, FIG. 1 illustrates a cross-sectional view of a conventional light emitting diode. The light emitting diode comprises a substrate 100, a n-type semiconductor buffer layer 102, a n-type semiconductor contact layer 104, a n-type semiconductor cladding layer 106, an active layer 108, a p-type semiconductor cladding layer 110 and a p-type semiconductor contact layer 112 stacked in sequence. The light emitting diode further comprises a p-type contact pad 114 located on a portion of the p-type semiconductor contact layer 112, and a n-type contact pad 116 located on the exposed portion of the n-type semiconductor contact layer 104. [0004] The material of the substrate 100 of a conventional light emitting diode adopts n-type gallium arsenide (GaAs). The substrate 100 composed of n-type GaAs can absorb light, so that most of the photons produced by the active layer 108 of the light emitting diode while emitting toward the substrate 100 are absorbed by the substrate 100, thus seriously affecting the light emitting efficiency of the light emitting diode device. [0005] In order to avoid the issue of light absorbed by the substrate, I. Pollentirer et al. in the Gent university in Belgium disclosed a technology in the journal "Electronics Letters" about directly bonding the GaAs light emitting diode wafer to the silicon (Si) substrate after the GaAs light emitting diode wafer is stripped off the GaAs substrate in 1990. Additionally, the U.S. Pat. No. 5,376,580 (application date: Mar. 19, 1993) filed by Hewlett-Packard Co., U.S.A. disclosed a technology about directly bonding the AlGaAs light emitting diode wafer to the other substrate after the AlGaAs light emitting diode wafer is stripped off the GaAs substrate. However, the U.S. Pat. No. 5,376,580 has a disadvantage of low yield caused by the need of considering the consistency of the lattice direction between the bonding wafers. Furthermore, the U.S. Pat. No. 6,258,699 (application date: May 10, 1999) filed by K. H. Chang et al., Visual Photonics Epitaxy Co., R.O.C. disclosed a technology about using metal as a bonding agent after the light emitting diode wafer is stripped off the growth substrate. However, a disadvantage of the U.S. Pat. No. 6,258,699 is that: the light emitting diode wafer is easy to peel off after bonding, thus lowering the yield. SUMMARY OF THE INVENTION [0006] An objective of the present invention is to provide a light emitting diode having a transparent substrate, wherein a surface of the substrate having a reflective layer with high light reflection. Therefore, the loss of light absorbed by the substrate can be reduced, and the reuse of the photons can be provided, so as to increase the quantity of the photons extracted from lateral sides of the device. [0007] Another objective of the present invention is to provide a light emitting diode, wherein a n-type contact pad of the light emitting diode is located on the front side of the device, so that the light emitting diode has a better current-spreading effect. [0008] Still another objective of the present invention is to provide a light emitting diode, and a transparent conductive layer can be formed to cover the n-type contact layer after etching, thereby increasing light extraction efficiency and keeping a better current-spreading effect. [0009] According to the aforementioned objectives of the present invention, the present invention provides a light emitting diode comprising: a transparent substrate; a reflective layer located on a surface of the transparent substrate; a solder layer located on the other surface of the transparent substrate; a semiconductor epitaxial structure located on the solder layer, wherein the semiconductor epitaxial structure comprises a p-type semiconductor contact layer, a p-type semiconductor cladding layer, a multiple quantum well active layer, a n-type semiconductor cladding layer and a n-type semiconductor contact layer stacked in sequence, and the p-type semiconductor layer contacts the solder layer; and a transparent conductive layer located on the semiconductor epitaxial structure. [0010] According to a preferred embodiment of the present invention, the n-type semiconductor contact layer can be a continuous surface structure. Alternatively, the n-type semiconductor contact layer can be a discontinuous surface structure, and the discontinuous surface structure can be a cylinder structure or a prism structure. [0011] The loss of light intensity resulted from the absorbing of the substrate can be reduced greatly by removing the growth substrate. Besides, the yield can be increased and the production cost can be reduced by using a solder material to perform a wafer bonding step. Furthermore, the reflective layer on the transparent substrate can provide reuse of photons to increase the quantity of the photons extracted from the lateral side of the device. In addition, depositing a transparent conductive layer on the etched n-type semiconductor contact layer not only can increase light extraction efficiency, but also can maintain current-spreading effect. BRIEF DESCRIPTION OF THE DRAWINGS [0012] The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: [0013] FIG. 1 illustrates a cross-sectional view of a conventional light emitting diode. [0014] FIG. 2 to FIG. 5a are schematic flow diagrams showing the process for manufacturing a light emitting diode in accordance with a preferred embodiment of the present invention. [0015] FIG. 5b illustrates a cross-sectional view of a light emitting diode in accordance with another preferred embodiment of the present invention. [0016] FIG. 6 illustrates a schematic diagram showing light extraction directions of a light emitting diode in accordance with a preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT [0017] The present invention discloses a light emitting diode. In order to make the illustration of the present invention more explicitly and completely, the following description and the drawings from FIG. 2 to FIG. 6 are stated. [0018] Among semiconductor light emitting devices, AlGaInP is a very commonly-used material. Because AlGaInP is a kind of direct bandgap materials, appropriately adjusting the ratio of In/(Al+Ga) in the AlGaInP material can make the lattice constant of the AlGaInP material and the GaAs substrate matched. Adjusting the ratio of Al and Ga in the AlGaInP material can make light emitted between 550 nm (green light) and 680 nm (red light) in wavelength. It is very easy to adjust the AlGaInP material on the device epitaxy, so it is easy to obtain emitting light with desired wavelengths by a linear method, and AlGaInP is very suitable for use in manufacturing a light emitting device of visible light zone. 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